CZ SP-01 9mm Magazines

Hello, all. I recently purchased a CZ SP-01 Tactical 9mm. It is my first CZ and I love it. I'm a .45 guy, but I wanted an accurate 9mm for target shooting. I've had other 9mm's before, but this gun is unbelievable. Accurate as hell. The ergonomics and inherent accuracy remind me of a 1911.

The pistol came with two 18 round mags, making the gun 18+1. I keep reading people writing about 19 round mags, but haven't seen these mags anywhere. Is the 19 rounder a non CZ made mag? What gives?